The present invention relates to an arrangement for controlling a plurality of light-emitting diodes which are connected in series, such a series connection being referred to as LED chain; at least two of said LED chains are connected in parallel to each other and are connected to a constant current source with respectively one first end of the LED chain, wherein the LED chains with the second ends thereof are at least indirectly connected to a second end of the constant current source via a correspondingly associated controllable semiconductor switch.
The invention also relates to a method for controlling a plurality of light-emitting diodes which are connected in series being referred to as LED chain, wherein a provided total current I is divided into a first partial current Ia associated with a first LED chain and a second partial current Ib associated with a second LED chain, wherein a first means for current control of the first partial current Ia is provided in series connection with the first LED chain, and a second means for current control of the second partial current Ib in provided in series connection with the second LED chain.
In many fields of electronics, light-emitting semiconductor diodes, also referred to as light-emitting diodes or briefly LEDs, are employed to realize display or lighting functions. This applies in particular to the field of automotive engineering, where light-emitting diodes are designed to replace the hitherto used light bulbs, for instance both in the field of motor vehicle interior applications, instrument panel lighting and in the field of prescribed standard lighting devices.
The special advantages of light-emitting diodes compared to conventional light bulbs can be seen in low power consumption, high luminous efficiency, relatively low heat generation as well as long service life. Moreover, light-emitting diodes do not have a starting delay and provide a smooth dimming function.
For this purpose, several solutions are known from prior art. In addition to the utilization of a current-limiting series resistance, regulated constant current sources as well as linear controllers are employed.
Arrangements, in which several LEDs are connected in series, are equally known, for instance to enhance light intensity. In this case too, current control and/or current limitation of the current flowing through all LEDs of the series connection is/are necessary.
When using a constant current source for providing a regulated operating current for the LEDs, the number of LEDs which can be arranged in the series connection is limited, in particular due to the supply voltage available in a motor vehicle. Conventional supply voltages lie in the range of for instance 12V for motor vehicles, 24V for trucks and 48V for electric and hybrid motor vehicles. If light intensity, which can be generated by means of an LED series connection, which is also referred to as LED chain, is insufficient, provision has to be made for at least one additional LED chain. Each additional LED chain, in turn, necessitates a separate constant current source, whereby expenditure and costs in connection with the entire lighting system are increased.
Alternatively, according to prior art, several LED chains can be operated in parallel connection with a single voltage source, whereby each LED chain requires a controller for current limitation. Said controller is respectively connected in series with the corresponding LED chain. In this case too, costs are increased due to the necessity of several controllers for several LED chains. Moreover, voltage drop along with corresponding electrical losses as well as unwanted heat development of the controller occur via each controller, also in an operating state, where the controller is fully controlled.
US patent publication 2011/0080115 A1 discloses an arrangement for generating constant partial currents for controlling several LEDs (LED chain) which are connected in series. Said arrangement has several outlets which have LED chains connected thereto. It is provided that the total current I generated by a constant current source is distributed to the LED chains which are connected in parallel with the constant current source. For this purpose, each LED chain is connected in series with a separate current divider arrangement, wherein each current divider arrangement is connected to a separate control arrangement for controlling the partial current through the LED chain.
US patent publication 2012/0268021 A1 describes a multi-channel LED driver arrangement for LED chains. Said arrangement comprises inter alia a power supply unit, a rectifier and filter unit, several LED chains, linear controllers, controllers and PWM units. It is the object of the arrangement to provide uniform currents to the LED chains being connected to the power supply, in order to thereby prevent for instance brightness differences between the LED chains.
Each LED chain is provided with a linear controller, which regulates the current of the connected LED chain. This regulator operates for instance with a MOSFET switch, which is controlled via an associated controller.
US patent publication 2013/0119873 A1 discloses an arrangement and a method for operating an LED backlighting. Said arrangement comprises a plurality of LEDs of a backlighting, which are connected in series, an associated driver, a current divider as well as a power supply unit. It is disclosed that the drivers are each connected in series with respectively one LED chain and control the current flowing through said LED chain. The LED chains are supplied via a common voltage supply unit.
The drawbacks resulting from said known prior art thus reside in high circuitry-related expenditure for several constant current sources, respectively necessary units for current regulation and the thusly associated high costs. Moreover, longitudinal controllers also always cause a voltage drop in the series connection along with electrical losses and heat generation, which under certain circumstances necessitates further cooling measures.
It would therefore be desirable and advantageous to provide an improved arrangement and method for controlling a plurality of light emitting diodes connected in series to obviate prior art shortcomings.